Bucket drum with moving vanes

grabcad

The proposed concept is based on the idea of having the drum divided into several internal “chambers” by means of some movable vanes that open/close the inlet ports of the scoops according to the drum angular position. The vanes are constrained to some supports on the bucket, in order to have that they are allowed to move only in the drum radial direction. The movement of the vanes occurs thanks to a cam-like profile obtained on a stationary shaft (or camshaft), i.e. a shaft solid to the chassis of the Rassor and co-axial to the bucket drum. The radial movement of a vane according to the cam profile is allowed thanks to a small wheel, which rolls inside a guide following the cam profile, and is connected to the inner end of the vane (i.e, the extremity of the vane close to the bucket rotation axis) through a pin, that serves as rotation axis for the wheel. The cam profile is defined in such a way that inlet ports of the scoops are opened only in the angular interval of interest to allow regolith collection (with clockwise rotation) and regolith damp (with anti-clockwise rotation). The guide obtained on the cam is protected by a cover and a seal in order to avoid that the regolith may generate obstacles to the wheels rolling along the cam profile.This design allows to maximize the inner volume of the bucket drum that can be filled with regolith while avoiding that the material collected by a scoop is unintentionally expelled during the drum rotation or while the Rassor hauls to the damp location. Moreover, the periodic opening/closing of the ports allow to remove mud or other obstacles that may accumulate on the port, thus contributing to avoid the clogging of the inlets.The bucked-drum itself is made by a thin layer of carbon-fiber, and the drum bases are supported by an aluminum-alloy support with spokes. The entire design is fully modular. In order to allow the installation of several buckets in a row, the camshaft itself is modular: each bucket drum unit has a unitary component of the camshaft, and the entire camshaft is composed by assembling one to the other several camshaft units. The camshaft is a hollow shaft that hosts some bearings, which support the main rotating driveshaft. The rotating driveshaft has a geared end to connect to the motor in the Rassor arm, while the other end of the shaft is connected through screws to the aluminum structure of the outer bucket drum.Each scoop is endowed with a “cutting edge” in steel or titanium, and with a grid in order to allow the collection of small regolith only. Each element of the grid is wedge-shaped, which would cut possible “mud” (in case of regolith with ice or water) thus contributing to avoid clogging. Optionally, the cutting edge may include also a backward extension (which would thus cover part of the carbon-fiber on the bucket side) with a “scraping surface”, in order to prepare the surface to the excavation between one port and the following.The proposed final assembly includes 3 bucket modules assembled in a row, with 3 scoops per bucket, each bucket being about 110 mm width, for a total width of 331 mm and an outer diameter of 450 mm. Scoops are positioned with an angular distance of 40° one from the other, therefore a single scoop is engaged at a time. The useful inner volume of each drum is 14.9 liters, for a total displacement of 44.7 liters for the three-buckets assembly. With an expected fill ratio of 80%, the assembly would allow 35.8 liters of regolith to be collected. Considering the entire bucket assembly (including buckets, supports, camshaft, blades, cam-guide wheels, cam covers, cutting edges), and excluding the driveshaft and the means of connection of the camshaft to the Rassor chassis, the total weight of the assembly is 5 kg. In order to comply with the weight limit, the amount of bucket units to be assembled was limited to 3, and the total volume of the assembly is smaller than the maximum allowed volume. Moreover, still for weight compliance, the cutting edge included in the final assembly do not include the scraping surface. An example of the cutting edge with scraping surface is also provided in STL format.